Effect of NBO on brain edema formation and BBB permeability after 90-min MCAO with 22.5-hr reperfusion. A) Representative brain sections of the normoxic, NBO-, vehicle- and apocynin-treated rats. Significant right (ischemic) hemispheric enlargement is seen in rats of all groups. B) Quantitative image analysis showed a significant reduction of hemispheric enlargement in the NBO- or apocynin-treated rats when compared to normoxic rats. Data are expressed as mean ±SEM, n = 4 in the vehicle-treated group, n = 7 in each of other three groups. *P < 0.05 versus normoxic rats. C) Effect of NBO on BBB permeability coefficient assessed by MRI based technique. A significant increase was observed for BBB permeability coefficient in the ischemic hemisphere of both normoxic and NBO-treated rats (*P < 0.05 versus nonischemic hemisphere). NBO significantly reduced BBB permeability in the ischemic hemisphere (#P < 0.05 versus normoxic rats). Data are expressed as mean ± SEM, n = 6 in each group.